The present invention relates in general to a solid state image sensing device and, in more particular, to a CCD image sensor which is swing-driven to relatively and periodically shift in position relative to incident image light.
In a conventional solid state image sensor such as an interline transfer type CCD (to be referred to as an IT-CCD hereinafter), it is easily understood that the number of pixels must be increased to obtain a high resolution of a video image in accordance with an interlaced scanning technique. However, even such a conventional IT-CCD having a standard number of pixels has the largest chip size among LSIs. If the number of pixels is simply increased in such a CCD to satisfy the need for high resolution, its chip size is further increased. On the other hand, in order to increase the number of pixels without changing the present CCD chip size, the integration of pixels must be greatly enhanced (e.g., more than 4 times). It is technically difficult to prepare such a high-density CCD. Even if development of improved fabrication techniques allows the manufacture of such a CCD in the near future, the circuit configuration for driving such a CCD becomes complicated and power consumption becomes high, thus entailing new problems.
In order to solve the problem concerning the number of pixels vs packing density, the CCD is periodically displaced relative to incident image light, thereby picking up a high-resolution image. In two field periods constituting one frame period in the NTSC system, when the CCD is swung at an amplitude corresponding to 1/2 the pixel pitch (PH) such that pixels are positioned in different sampling positions along a horizontal direction, the spatial sampling points along the horizontal direction can be virtually increased. Therefore, the horizontal resolution of the one-frame image can be substantially doubled even if a conventional low-resolution IT-CCD chip is used.
According to this swing image pickup technique, however, the number of spatial sampling pixels along a single scanning line on a one-field screen is the same as that of a real array of pixels of the CCD and cannot be doubled. When an A field screen is combined with a B field screen obtained such that every other scanning line is scanned and a given scanned pixel on an A-field scanning line is offset by 1/2 a pitch from a corresponding scanned pixel on a B-field scanning line, so that the A and B fields constitutes a one-frame picture, a high-contrast image profile line (white/black boundary line), especially a profile line extending vertically on the screen, is observed as a zigzag line in a one-frame picture. It is undesirable that an originally linear (or curved) smooth profile portion becomes a zigzag line, thus degrading the image quality.